Yamei Niu

The role of Fat Mass and Obesity-associated protein (FTO) and its substrate N6-methyladenosine (m6A) in mRNA processing and adipogenesis remains largely unknown. We show that FTO expression and m6A levels are inversely correlated during adipogenesis. FTO depletion blocks differentiation and only catalytically active FTO restores adipogenesis. Transcriptome analyses in combination with m6A-seq revealed that gene expression and mRNA splicing of grouped genes are regulated by FTO. M6A is enriched in exonic regions flanking 5'- and 3'-splice sites, spatially overlapping with mRNA splicing regulatory serine/arginine-rich (SR) protein exonic splicing enhancer binding regions. Enhanced levels of m6A in response to FTO depletion promotes the RNA binding ability of SRSF2 protein, leading to increased inclusion of target exons. FTO controls exonic splicing of adipogenic regulatory factor RUNX1T1 by regulating m6A levels around splice sites and thereby modulates differentiation. These findings provide compelling evidence that FTO-dependent m6A demethylation functions as a novel regulatory mechanism of RNA processing and plays a critical role in the regulation of adipogenesis.

N(6)-methyl-adenosine (m(6)A) is one of the most common and abundant modifications on RNA molecules present in eukaryotes. However, the biological significance of m(6)A methylation remains largely unknown. Several independent lines of evidence suggest that the dynamic regulation of m(6)A may have a profound impact on gene expression regulation. The m(6)A modification is catalyzed by an unidentified methyltransferase complex containing at least one subunit methyltransferase like 3 (METTL3). m(6)A modification on messenger RNAs (mRNAs) mainly occurs in the exonic regions and 3'-untranslated region (3'-UTR) as revealed by high-throughput m(6)A-seq. One significant advance in m(6)A research is the recent discovery of the first two m(6)A RNA demethylases fat mass and obesity-associated (FTO) gene and ALKBH5, which catalyze m(6)A demethylation in an α-ketoglutarate (α-KG)- and Fe(2+)-dependent manner. Recent studies in model organisms demonstrate that METTL3, FTO and ALKBH5 play important roles in many biological processes, ranging from development and metabolism to fertility. Moreover, perturbation of activities of these enzymes leads to the disturbed expression of thousands of genes at the cellular level, implicating a regulatory role of m(6)A in RNA metabolism. Given the vital roles of DNA and histone methylations in epigenetic regulation of basic life processes in mammals, the dynamic and reversible chemical m(6)A modification on RNA may also serve as a novel epigenetic marker of profound biological significances.

N6-methyladenosine (m6A) is an important epitranscriptomic mark with high abundance in the brain. Recently, it has been found to be involved in the regulation of memory formation and mammalian cortical neurogenesis. However, while it is now established that m6A methylation occurs in a spatially restricted manner, its functions in specific brain regions still await elucidation. We identify widespread and dynamic RNA m6A methylation in the developing mouse cerebellum and further uncover distinct features of continuous and temporal-specific m6A methylation across the four postnatal developmental processes. Temporal-specific m6A peaks from P7 to P60 exhibit remarkable changes in their distribution patterns along the mRNA transcripts. We also show spatiotemporal-specific expression of m6A writers METTL3, METTL14, and WTAP and erasers ALKBH5 and FTO in the mouse cerebellum. Ectopic expression of METTL3 mediated by lentivirus infection leads to disorganized structure of both Purkinje and glial cells. In addition, under hypobaric hypoxia exposure, Alkbh5-deletion causes abnormal cell proliferation and differentiation in the cerebellum through disturbing the balance of RNA m6A methylation in different cell fate determination genes. Notably, nuclear export of the hypermethylated RNAs is enhanced in the cerebellum of Alkbh5-deficient mice exposed to hypobaric hypoxia. Together, our findings provide strong evidence that RNA m6A methylation is controlled in a precise spatiotemporal manner and participates in the regulation of postnatal development of the mouse cerebellum.

RNA modification meets immune metabolism N 6 -methyladenosine (m 6 A) RNA modification regulates various cellular functions. Liu et al. found that host cells impair RNA m 6 A demethylase activity after viral infection, leading to increased m 6 A and reduced stability of α-ketoglutarate dehydrogenase (OGDH) mRNA. As a result, reduced OGDH decreases the generation of itaconate, thereby inhibiting viral replication. The authors explore the function of OGDH and itaconate in viral infection, provide insights into m 6 A RNA modification and metabolic reprogramming in modulating virus-host interaction, and suggest potential therapeutic targets for the control of viral infection. Science , this issue p. 1171